The present invention relates to a printer, copier, facsimile apparatus or similar image forming equipment which heats a charged image carrier in association with an image to attenuate part of the potential thereof to thereby form a latent image and develops the latent image to produce a visible image.
Image forming equipment extensively used today uses an electrophotographic procedure which charges an image carrier in the form of a photoconductive element, illuminates the charged image carrier by a laser beam representative of document information to electrostatically form a latent image, develop the latent image by a liquid toner or a dry toner to produce a toner image, and transfer the toner image to a paper sheet or similar recording medium. The problem with this type of image forming equipment is that the photoconductive element and an optical unit for exposing it are expensive, increasing the overall cost of the equipment. Another problem is that the optical unit has to be sufficiently screened from external light in order to illuminate only part of the photoconductive element which corresponds to an image. This not only increases the number of parts but also complicates the construction, further increasing the cost of the equipment.
On the other hand, there has been proposed an image forming method which heats a charged image carrier in association with an image to attenuate part of the potential thereof to thereby form a latent image and develops the latent image to produce a visible image, as disclosed in, for example, Japanese Patent Publication Nos. 14722/1960 and 15878/1962. This type of equipment forming a latent image by heat is operable with an image carrier which is far lower in cost than a photoconductive element, and a thermal writing unit which is also far lower in cost than an optical unit. In addition, such equipment does not need a screening implementation. However, this type of equipment has customarily relied only on the drop of electric resistance of the image carrier due to heat. Moreover, such equipment has not given consideration to the stable formation of a latent image or the durability of the image carrier against repetitive use.